Wind turbines are provided with a rotor shaft which is part of an electrical generator producing electricity during movement of the rotor relative to a stator of the generator. The stator comprises a number of coils, the rotor comprises a number of permanent magnets so that an electric voltage is induced when the rotor is turned.
Wind turbines must be aligned optimally to the wind in order to prevent extreme loads and to provide the highest possible energy output. In order to control the power output of the wind turbine, the blade angle is always optimally adjusted to the wind speed via the blade bearing. High loads must be transferred securely via the bolted connection into the rotor hub.
Conventionally fasteners in the form of bolts, nuts and washers are used to join two or more structural components, e.g. for connecting a rotor blade to a blade bearing. As wind turbines experience a dynamic loading conventional bolted connections suffer from fatigue damage and ultimately fatigue failure can occur. In the past a number of fatal collapses have occurred, therefore the correct dimensioning of bolted connections, in particular for connecting the rotor blade to the blade bearing, is of prime importance.
The most common solution for the problem of fatigue failure is simply to add more and larger bolts. However, this is of course not an economically sensible solution. Therefore in wind turbines with large rotor diameters the bolted connection between rotor blade and blade bearing has become the dimensioning factor for the blade root design, since no more bolts can be added.